In traditional dress, a member of the Vietnamese community attends a ceremony on the flight deck of the USS Midway as the ship hosts a commemoration of the 40th Anniversary of Operation Frequent Wind and the fall of Saigon in San Diego, California, United States April 26, 2015. Volunteers tied 58,300 yellow ribbons on a fence surrounding the Midway's flight deck to signify U.S. deaths in the conflict. (Photo by Mike Blake/Reuters)

Former Vietnamese military position a vintage jeep near the USS Midway during a day-long ceremony commemorating the 40th Anniversary of Operation Frequent Wind and the fall of Saigon in San Diego, California, United States April 26, 2015. (Photo by Mike Blake/Reuters)

Visiting members of the Vietnamese community pose for a picture in front of antique military jeeps as they arrive to attend a ceremony on the flight deck of the USS Midway commemorating the 40th Anniversary of Operation Frequent Wind and the fall of Saigon in San Diego, California, United States April 26, 2015. (Photo by Mike Blake/Reuters)

A Vietnam veteran wears patches and pins on his jacket as he attends the USS Midway's ceremony commemorating the 40th Anniversary of Operation Frequent Wind and the fall of Saigon in San Diego, California, United States April 26, 2015. (Photo by Mike Blake/Reuters)

Performers do a traditional Vietnamese dance as the USS Midway hosts a day-long ceremony commemorating the 40th Anniversary of Operation Frequent Wind and the fall of Saigon in San Diego, California, United States April 26, 2015. (Photo by Mike Blake/Reuters)

A young Vietnamese boy looks at some of the 58,300 yellow ribbons tied to a fence surrounding the flight deck of the USS Midway as the ship commemorates the 40th Anniversary of Operation Frequent Wind and the fall of Saigon in San Diego, California, United States April 26, 2015. (Photo by Mike Blake/Reuters)

Visiting members of the Vietnamese community take pictures as they attend a ceremony on the flight deck of the USS Midway as the ship commemorates the 40th Anniversary of Operation Frequent Wind and the fall of Saigon in San Diego, California, United States April 26, 2015. (Photo by Mike Blake/Reuters)

Tradition Vietnamese dancing is performed as the USS Midway hosts a day-long ceremony commemorating the 40th Anniversary of Operation Frequent Wind and the fall of Saigon in San Diego, California, United States April 26, 2015. (Photo by Mike Blake/Reuters)

Visiting members of the Vietnamese community attend a ceremony on the flight deck of the USS Midway as the ship commemorates the 40th Anniversary of Operation Frequent Wind and the fall of Saigon in San Diego, California, United States April 26, 2015. (Photo by Mike Blake/Reuters)

A man looks over the names on a traveling exhibition of “The Wall That Heals”, a half-size replica of the Vietnam War Memorial Wall in Washington, D.C during a ceremony aboard the USS Midway commemorating the 40th Anniversary of Operation Frequent Wind and the fall of Saigon in San Diego, California, United States April 26, 2015. (Photo by Mike Blake/Reuters)

A U.S. veteran looks at some of the 58,300 yellow ribbons tied on a fence surrounding the Midway's flight deck to signify U.S. deaths in the Vietnam war as the Midway hosts a day-long ceremony commemorating the 40th Anniversary of Operation Frequent Wind and the fall of Saigon in San Diego, California, United States April 26, 2015. (Photo by Mike Blake/Reuters)

Former Vietnamese military men throw a memorial reef off the deck of the USS Midway as the ship hosts a day-long ceremony commemorating the 40th Anniversary of Operation Frequent Wind and the fall of Saigon in San Diego, California, United States April 26, 2015. (Photo by Mike Blake/Reuters)

A visiting member of the Vietnamese community takes her own picture as she attends a ceremony on the flight deck of the USS Midway to commemorate the 40th anniversary of Operation Frequent Wind and the fall of Saigon in San Diego, California, United States April 26, 2015. (Photo by Mike Blake/Reuters)

Visiting members of the Vietnamese community wave U.S. flags and the flag of former South Vietnam as they attend a ceremony on the flight deck of the USS Midway as the ship commemorates the 40th Anniversary of Operation Frequent Wind and the fall of Saigon in San Diego, California, United States April 26, 2015. (Photo by Mike Blake/Reuters)

The flag of former South Vietnam is draped over the shoulders of Vietnamese refugee Bai-Binh Ton-Thap as he prays next to some of the 58,300 yellow ribbons tied to a fence surrounding the flight deck of the USS Midway as the ship commemorates the 40th Anniversary of Operation Frequent Wind and the fall of Saigon in San Diego, California, United States April 26, 2015. (Photo by Mike Blake/Reuters)

Vietnamese soldiers adjust medals for their comrades during a rehearsal for a military parade as part of the 40th anniversary of the fall of Saigon in southern Ho Chi Minh City (formerly Saigon City), Vietnam, on April 26, 2015. Vietnam marks the 40th anniversary of the fall of Saigon on April 30, the event that ended a war that lasted over 30 years, killing up to four million Vietnamese, the Vietnamese government said, and more than 58,000 U.S troops, the U.S. Department of Defense has said. (Photo by Reuters/Kham)

Vietnamese military soldiers attend a rehearsal for a military parade as part of the 40th anniversary of the fall of Saigon in southern Ho Chi Minh City (formerly Saigon City), Vietnam, on April 26, 2015. (Photo by Reuters/Kham)

Vietnamese military soldiers carry flags with medals while marching during a rehearsal for a military parade as part of the 40th anniversary of the fall of Saigon in southern Ho Chi Minh City (formerly Saigon City), Vietnam, on April 26, 2015. (Photo by Reuters/Kham)

Vietnamese village policemen walk in front of the Unification Palace (formerly Presidential Palace) after a rehearsal for a military parade as part of the 40th anniversary of the fall of Saigon in southern Ho Chi Minh City (formerly Saigon City), Vietnam, on April 26, 2015. (Photo by Reuters/Kham)

Vietnamese female paramilitary personnel take part during a rehearsal for a military parade as part of the 40th anniversary of the fall of Saigon in southern Ho Chi Minh City (formerly Saigon City), Vietnam, on April 26, 2015. (Photo by Reuters/Kham)

Vietnamese soldiers of border guard force march during a rehearsal for a military parade as part of the 40th anniversary of the fall of Saigon in southern Ho Chi Minh City (formerly Saigon City), Vietnam, on April 26, 2015. (Photo by Reuters/Kham)

Students wave the Vietnamese national flag during a rehearsal for a military parade as part of the 40th anniversary of the fall of Saigon in southern Ho Chi Minh City (formerly Saigon City), Vietnam, on April 26, 2015. (Photo by Reuters/Kham)

Vietnamese workers march during a rehearsal for a military parade as part of the 40th anniversary of the fall of Saigon in southern Ho Chi Minh City (formerly Saigon City), Vietnam, on April 26, 2015. (Photo by Reuters/Kham)

Vietnam's Defence Minister General Phung Quang Thanh (R) talks with soldiers attending a rehearsal for a military parade as part of the 40th anniversary of the fall of Saigon in southern Ho Chi Minh City (formerly Saigon City), Vietnam, on April 26, 2015. (Photo by Reuters/Kham)

Vietnamese Navy sailors march during a rehearsal for a military parade as part of the 40th anniversary of the fall of Saigon in southern Ho Chi Minh City (formerly Saigon City), Vietnam, on April 26, 2015. (Photo by Reuters/Kham)

Vietnamese policemen march during a rehearsal for a military parade as part of the 40th anniversary of the fall of Saigon in southern Ho Chi Minh City (formerly Saigon City), Vietnam, on April 26, 2015. (Photo by Reuters/Kham)

Vietnamese female soldiers march during a rehearsal for a military parade as part of the 40th anniversary of the fall of Saigon in southern Ho Chi Minh City (formerly Saigon City), Vietnam, on April 26, 2015. (Photo by Reuters/Kham)

Vietnamese female traffic police officers march during a rehearsal for a military parade as part of the 40th anniversary of the fall of Saigon in southern Ho Chi Minh City (formerly Saigon City), Vietnam, on April 26, 2015. (Photo by Reuters/Kham)

Vietnamese village policemen joke during a rehearsal for a military parade as part of the 40th anniversary of the fall of Saigon in southern Ho Chi Minh City (formerly Saigon City), Vietnam, on April 26, 2015. (Photo by Reuters/Kham)

Vietnamese farmers march during a rehearsal for a military parade as part of the 40th anniversary of the fall of Saigon in southern Ho Chi Minh City (formerly Saigon City), Vietnam, on April 26, 2015. (Photo by Reuters/Kham)

Vietnamese workers march during a rehearsal for a military parade as part of the 40th anniversary of the fall of Saigon in southern Ho Chi Minh City (formerly Saigon City), Vietnam, on April 26, 2015. (Photo by Reuters/Kham)

Students form the Vietnamese national flag during a rehearsal for a military parade as part of the 40th anniversary of the fall of Saigon in southern Ho Chi Minh City (formerly Saigon City), Vietnam, on April 26, 2015. (Photo by Reuters/Kham)

Fire-fighters march during a rehearsal for a military parade as part of the 40th anniversary of the fall of Saigon, in southern Ho Chi Minh City (formerly Saigon City), Vietnam, April 26, 2015. (Photo by Reuters/Kham)

Members of a military patrol keep guard in front of the Reunification Palace, formerly the presidential palace, during a rehearsal for a military parade as part of the 40th anniversary of the fall of Saigon, in southern Ho Chi Minh City (formerly Saigon City), Vietnam, April 26, 2015. (Photo by Reuters/Kham)

A man drives a mock military Tank 390, which was operated by North Vietnamese forces and first crashed through the gate of the former presidential palace, during a rehearsal for a military parade as part of the 40th anniversary of the fall of Saigon, in southern Ho Chi Minh City (formerly Saigon City), Vietnam, April 26, 2015. (Photo by Reuters/Kham)

Soldiers attend a rehearsal for a military parade as part of the 40th anniversary of the fall of Saigon, in southern Ho Chi Minh City (formerly Saigon City), Vietnam, April 26, 2015. (Photo by Reuters/Kham)

Special forces soldiers march during a rehearsal for a military parade as part of the 40th anniversary of the fall of Saigon, in southern Ho Chi Minh City (formerly Saigon City), Vietnam, April 26, 2015. (Photo by Reuters/Kham)

Soldiers of the marine patrol force march during a rehearsal for a military parade as part of the 40th anniversary of the fall of Saigon, in southern Ho Chi Minh City (formerly Saigon City), Vietnam, April 26, 2015. (Photo by Reuters/Kham)

A man pushes a mock military Tank 390, which was operated by North Vietnamese forces and first crashed through the gate of the former presidential palace, past the palace after a rehearsal for a military parade as part of the 40th anniversary of the fall of Saigon, in southern Ho Chi Minh City (formerly Saigon City), Vietnam, April 26, 2015. (Photo by Reuters/Kham)

Southern Vietnamese female paramilitants march during a rehearsal for a military parade as part of the 40th anniversary of the fall of Saigon, in southern Ho Chi Minh City (formerly Saigon City), Vietnam, April 26, 2015. (Photo by Reuters/Kham)

Performers wave the flags of Vietnam's National Liberation Front during a rehearsal for a military parade as part of the 40th anniversary of the fall of Saigon, in southern Ho Chi Minh City (formerly Saigon City), Vietnam, April 26, 2015. (Photo by Reuters/Kham)